kennythekey
The wall is a bearing wall that sits on the foundation wall, so it’s not wiggly! The rack can only rock forwards and backwards, so much more stable side-to-side. If I stomp/jump in front of it, I can get the stylus to skip. Otherwise, not a problem, so it’s a safety issue.
As fate would have it it’s not only floors that are the problem but also walls and ceilings, they all transmit seismic type vibrations. Unsuspended floors might be more problematic, what with trampoline effect and greater susceptibility to seismic type vibrations, including footfall and mechanical feedback, but even cement slabs and bearing walls on rigid foundations are moving, just not with the same amplitude usually. In areas like Las Vegas where there is rather strong Earth motion you can feel the vibration on the walls with the palm of your hand. Most places you can’t feel it with your hand but it’s there, especially the very low frequency stuff, the stuff below 10 Hertz. That’s because the entire building is being moved and shaken by the Earth’s crust motion and anything else around like wind or traffic or subways. And it’s being shaken and moved in 6 different directions due to the way physical seismic waves travel along the surface of the Earth. Thus, the house is moving up and down, to and fro, back no forth as well as twisted, etc. Most of the energy of the Earth crust motion is down around 0 to 3 Hz, but there is still a lot up to 20 Hz and above. This of course means that in order to escape at least some of the seismic type vibration one needs to decouple from the physical surroundings entirely, including walls. Furthermore the effects of seismic type vibration don’t necessarily manifest themselves overtly, e.g., needle jumping from the groove, it can be more subtle and insidious. You don’t know what you got til it’s gone, like the song says.